In transmission devices known from practice, such as automatic transmissions, frictional shifting elements are increasingly often replaced by interlocking shifting elements in order to reduce the drag losses that occur in the area of frictional shifting elements. In this, however, it is problematic that during unfavorable operating conditions of a vehicle drive-train, an interlocking shifting element that has to be disengaged during a gearshift can still be under stress and it cannot then be disengaged to the desired extent.
For example, such stressing of an interlocking shifting element occurs during gearshifts in which the interlocking shifting element has to be disengaged from the force flow of a vehicle drive-train and at the same time a frictional shifting element has to be engaged in the force flow of the vehicle drive-train in order to produce the new gear ratio called for if, before the interlocking shifting element has had time to reach full disengagement, the frictional shifting element has built up a transmission capacity sufficient to impede the disengagement of the interlocking shifting element.
During such an operating condition sequence of a vehicle drive-train or of a transmission device, the possibility exists that in the area of the transmission device one or more gearsets will be stressed or blocked because of over-regulation, and with conventional procedures this can only be resolved by discontinuing the gearshift, or otherwise it results in un-reproducible shifting times.
Alternatively, stressing of the interlocking shifting element caused by engagement of the frictional shifting element and over-regulation in the area of the transmission device during a gearshift can be avoided by increasing the transmission capacity of the frictional shifting element only once the interlocking shifting element has been disengaged.
EP 1 344 965 A2 shows a method for operating a drive-train of a vehicle with a transmission device the comprises a frictional shifting element and a plurality of interlocking shifting elements. For a gearshift, an interlocking shifting element is disengaged and a frictional shifting element is engaged. If an engaged operating condition of the interlocking shifting element is detected, the after the lapse of a pre-defined time interval the shifting force is increased.
With such a procedure gearshifts can again not be carried out to the desired extent within pre-defined shifting times, so transmission devices can be operated even without reproducible shifting behavior.